The property possessed by some materials of improving detergency levels of soaps and synthetic detergents and the use of such materials in detergent compositions is known. Such cleaning boosters are called builders and such builders permit the attainment of better cleaning performance than is possible when so-called unbuilt compositions are used. The behavior and mechanisms by which builders perform their function are only partially understood. It is known that good builders must be able to sequester most of the calcium and/or magnesium ions in the wash water since these ions are detrimental to the detergency process. However, it is difficult to predict which class of compounds possess useful combinations of builder properties and which compounds do not because of the complex nature of detergency and the countless factors which contribute both to overall performance results and requirements of environmental acceptability.
Sodium tripolyphosphate (STPP) has been found to be a highly efficient cleaning and detergency builder and this compound has been widely used for decades in cleaning formulations. Indeed, millions of pounds of STPP are used each year in cleaning formulations because of its superior builder qualities. However, because of the recent emphasis on removing phosphates from detergent and cleaning compositions for environmental reasons, the detergent and cleaning industry is now looking for materials suitable for use as builders which do not contain phosphorus and which are environmentally acceptable.
Polymeric acetal carboxylates are suitable as a replacement for STPP in detergent compositions. The preparation of such polymeric acetal carboxylates has been disclosed in U.S. Pat. No. 4,144,226 issued Mar. 13, 1979 and in U.S. Pat. No. 4,204,052 issued May 20, 1980. The use of such polymeric acetal carboxylates in detergent compositions is disclosed in U.S. Pat. No. 4,146,496 issued Mar. 27, 1979. An improved method for the saponification of the esters of the polymeric acetal carboxylates to form the corresponding alkali metal salts is disclosed in U.S. Pat. No. 4,140,676 issued Feb. 20, 1979. An improved method of stabilizing the polymer against rapid depolymerization in alkaline solution by adding an alkyl vinyl ether in the presence of an organo aluminum compound is disclosed in U.S. Pat. No. 4,225,685 issued Sept. 30, 1980. The polymeric acetal carboxylate salts described in the above patents were tested for sequestration function using procedures described by Matzner et al. in "Organic Builder Salts as Replacements for Sodium Tripolyphosphate", TENSIDE, 10, No. 3 pages 119-125 (1973). As a result of such tests, polymeric acetal carboxylate salts were found to be superior detergent builders compared to STPP, and were stable under laundry use conditions but depolymerized at lower pH making the polymers more readily biodegradable.
Although the polymeric acetal carboxylates disclosed in the above patents are excellent sequestering agents and builders, it has now been found that these polymeric acetal carboxylates are subject to degradation of their sequestering capacity upon prolonged storage at elevated temperatures such as found in shipping and warehousing conditions in warm climates. It has now been found that solid compositions comprising polymeric acetal carboxylates in intimate admixture with an alkali metal carbonate are resistant to degradation and retain their sequestering capacity much longer under such storage conditions. In accordance with this invention such intimate admixtures are prepared by reacting an aqueous solution or slurry of the polymer and alkali metal hydroxide with carbon dioxide. This process is particularly advantageous in conjunction with the process of manufacturing the polymer by saponification of a polymeric ester precursor with excess alkali metal hydroxide. In this manner, at least some of the excess alkali metal hydroxide is converted to alkali metal carbonate which forms an intimate admixture with the polymer. Such admixtures can be readily recovered in solid form and are resistant to degradation during storage.